1. Field of the Invention
The present invention relates to a manufacturing method of an electric contact used for an electromagnetic switch, an electromagnetic contactor, a circuit breaker and the like, and relates to a manufacturing equipment of the electric contact.
2. Description of the Related Art
For example, an electric contact for an electromagnetic switch, an electromagnetic contactor and the like are configured such that a movable-side contact and a fixed-side contact are contacted and separated to/from each other so as to switch an electric circuit, thereby ON/OFF operation of electrical connection is performed. The contacts are connected to a movable-side metal base and a fixed-side metal base, each metal base having a predetermined shape, and supported thereby respectively.
As a method of joining a metal base and a contact together, a mechanical joining method and a welding method have been used in the past. The mechanical joining method includes caulking, cladding and the like. However, the mechanical joining method tends to be limitedly used for a joint having a small current capacity. Therefore, as a joint has a larger current capacity, a method using welding is increasingly needed, whereby joining area between a contact and a metal base can be adequately secured. The method using welding includes ultrasonic welding, resistance heating brazing, resistance spot brazing, resistance spot welding, furnace brazing, and high frequency induction brazing.
In welding, in the case of joining a relatively small contact (for example, a contact having area of width of 4.6 mm*height of 4.6 mm), a method using ultrasonic welding, and a method using resistance brazing or resistance spot brazing are generally used. In the case of welding, as a material of a contact, a Cd-based material typified by AgCdO/AgCd-based material, AgCdO/Ag-based material and the like, or a Cd-free material such as AgSnO2—In2SnO2/Ag-based material is used. In the light of mass productivity, ultrasonic welding is often used for the former, Cd-based material.
Recently, from the environmental consideration, a Cd-free contact containing no Cd is increasingly used, and the Cd-free material such as AgSnO2—In2SnO2/Ag-based material is now largely used. However, when such a Cd-free material is used for a small contact, and subjected to ultrasonic welding, a problem of fluctuation in joining strength occurs as compared with a contact using a Cd-based material. Moreover, in the case of the ultrasonic welding, joint quality between a contact and a metal base has been varied in some combination of a contact material and a metal base material, causing fluctuation in joining strength. When such fluctuation occurs in joining strength between the contact and the metal base, electric switching life of the contact may be affected. Consequently, the ultrasonic welding has been hardly used for mass production in some case.
Thus, the resistance brazing or the resistance spot brazing, which hardly affects joint quality, is used in some combination of a contact material and a metal base material. However, in this case, brazing filler metal needs to be used, causing a problem of increase in material cost, or increase in manufacturing cost due to a fact that a step needs to be added for inserting a brazing filler metal foil between a contact and a metal base. Furthermore, since the materials are heated to at least a melting temperature of brazing filler metal, the metal base is softened, causing a problem that the metal base must be subjected to some sort of treatment.
On the other hand, a joining technique called friction stir welding is now gradually used as a joining method for joining metal members to each other. In this technique, while a tool having a pin protrusively provided on an end face of the tool is rotated, the tool is pressed into a joint between members to be joined so as to generate frictional heat in the joint by rotation of the pin, so that the joint is stirred while being softened, causing plastic flow, and consequently the members are joined to each other via the plastic flow.
Katsuyuki Yoshikawa, ‘Micro Spot Friction Welding’, 11th Symposium MATE 2005, Japan Welding Society, 2005, pp. 421-424 (Non-Patent Document 1) discloses that, as a general principle of the friction stir welding, a tool is pressed into two sheets being superimposed while being rotated, and thereby the two sheets are joined by friction stir welding by using plastic deformation of a sheet material and frictional heat (that is, by using plastic flow). It is described that the plastic flow ranges over both the superimposed sheets, leading to welding of the two sheets.
JP-A-2006-21217 (Patent Document 1) discloses a friction stir welding apparatus for spot welding, which immerses a rotating joining tool into an object to be joined including a plurality of members to be joined for spot-welding the members to be joined to each other, includes a tool holding section that has a predetermined rotational axis, and holds the joining tool coaxially with the rotational axis; a rotational drive unit that drives to rotate the tool holding section around the rotational axis; a linear drive unit that drives the tool holding section to shift along the rotational axis; a base that supports the tool holding section; a laser beam generation unit for irradiating a condensed laser beam; and a control unit that controls the rotational drive unit, linear drive unit, and laser beam generation unit such that the laser beam is irradiated onto a portion to be joined formed on the object to be joined before the joining tool is immersed into the portion to be joined, so that the portion to be joined is heated to the softening temperature being lower than a melting point of the object to be joined, and high enough to soften the portion to be joined relatively to the joining tool.
Kinya AOTA ‘Spot Friction Stir Welding of Al/Cu’ (Whole Country Meeting of Japan Welding Society Lecture Abstract, September 2004) (Non-Patent Document 2), relating to a joining between an aluminum plate and a copper plate, mentions on the interfacial characteristics of the joining when a joining tool is pressed on top of a portion where the aluminum plate and the copper plate are overlapped. It, however, doesn't mention on the controlling of the depth of the pressing.
JP-A-S60-250891 (Patent Document 2) discloses a manufacturing method of an electric contact, which includes: forming a series of grooves having a certain pitch on a surface of a metal base; laying a piece of contact on the series of grooves; grasping while adding pressure the metal base and the piece of contact between a horn and an anvil with which an ultrasonic welding machine is equipped; and ultrasonic stirring a horn head in a direction aliened along the grooves, such that the piece of contact and the metal base can join each other.
JP-A-S55-006746 (Patent Document 3) discloses a manufacturing method of an electric contact, which includes: grasping while adding pressure a metal base and a contact between two electrodes; heating by allowing to pass electric current between the electrodes; and quick-chilling after the heating, such that the metal base and the contact can join each other.
JP-A-H10-269883 (Patent Document 4) discloses a manufacturing method of a contact member, which includes: forming in a metal base a crevice smaller than an outer diameter of a contact, the contact being made of a meltable material; laying the contact on the crevice, and welding and press-molding the contact laid on the crevice by use of a welding machine, such that the contact can be made to weld to the metal base in a predetermined shape.
JP-A-S58-186115 (Patent Document 5) discloses a manufacturing method of a silver/oxide type electric contact, which includes: inserting two of contact members between resistive electrodes by use of a resistance welding machine; pouring at least enough amount of an organic solvent to replace air in said inserted contact members; and adding pressure and allowing to pass electric current to thereby make a complex contact constituted by the two of contact members.
JP-A-S61-017394 (Patent Document 6) discloses a manufacturing method of a contact material, which includes: overlaying a first layer, the first layer consisting of a first component to constitute the contact material, to weld with a second layer, the second layer consisting of at least a second component, and being arranged to be in a thickness so as to become a predetermined composition of alloy when melting.
In the case of the above two types of friction stir welding, members are joined to each other by using plastic flow induced by friction stir of the members caused by rotation of the tool. However, since the tool needs to be pressed somewhat deep in order to join the two members together by using plastic flow, time required for joining has been increased, causing a problem in productivity. In addition, a dent or an impression caused by the tool has been sometimes conspicuous, causing a problem in quality.
Therefore, an object of the invention is to provide a manufacturing method of an electric contact, in which time required for joining together a contact and a metal base is short, and a dent or an impression can be suppressed to be formed on the contact, and provide manufacturing equipment of the electric contact.